Multistage hydraulic pump or motor



Sept. 1.2, 1939. E. K'. BENEDEK y 12,172,900

MULTISTAGE HYDRAULIC PUMP OR MOTOR v Filed Febjzs; 1935 5 sheets-sheet 1 om X9 Y s@ I le I I w ggg L 9) I' u) 5 N 'I 4%- i "J1 I Q Q f jj/ Il l l "I Ihn: l Ill@ Il l' 'u" l f! IJHI' @D 2 yI \9 N N mi' @w ,g '5.' o lq gf N k) I N I I? 0o o@ Q A 'i F1' F gj: lNvx-:NoR L ,1 ELEKKEENEDEK (Y if; BY

SePt- 12, 1939- E. K. BENEDEK 2,172,900

MULTISTAGE HYDRAULIC PUMP OR lMOTOR Filed Feb. 23, 1935 5 Sheets-Sheei*l 2 INVENTOR BYELEK KEI-:Nemax @ATTORNEY Sept. 12,1939. E. K. BENEDEK 2,172,900

MULTISTAGE HYDRAULIC PUMP 0RA MOTOR Filed Feb. 23, 1935 i l :lla

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MULTISTAGE HYDRAULIC PUMP OR MOTOR Filed Feb. 23, 1935v 5 Sheets-Sheet 4 INVENTOR BYELEKKEENEDEK- .ATTORNEY l Patented Sept. 12, l1939 UNITED STATES PATENTfOFFlCE 1 Claim.

'I'his invention relates to .radial piston type hydraulic pumps and motors and particularly to a compact and eieient multi-stage pump or motor unit of this character by which greater 3 ranges of4 both speed andtorque delivery and rapid changes in the relation therebetween may be obtained without the usual sacrifice in efficiency at the upper and lower limits of the range of operation and without appreciable loss of time l between changes in the stages of operation.

The present practice in connection. with hydraulic pumps and motors for comparatively Wide` ranges 'of operation is to provide two smaller pumping units instead of a single larger unit. This practice is due primarily to certain disadvantages inherent in large pumps and motors of specific examples, the larger pumps requirebearings and valve pintles of greater diameter, and

3 heavier piston and rotor parts, Thus,l witha larger diameter, not only is the peripheral speed of the bearings greatly increased for a given angular rotation, but also the centrifugal forces are disproportionately increased.`

u Further, due to the greater total .hydrostatic load that must be resisted by the pintle,

the greater overhang of the pintle that is re' quired and the greater ilow capacity which the pintle must accommodate, the pintle necessarily must be of considerably increased diameter in such larger pumps. This increase in diameter, in turn, results in much larger surfaces in fric-.tional engagement between the wall of the rotor bore and the valve pintle. Furthermore, due to the larger diameter of the pintle, there is not' only this greater frictional. surface engagement between the pintle and rotor bore wall but also a greater peripheral speed between these surfaces 50. for a given angular velocity of the rotor.

When operating at high speeds these frictional and centrifugal forces Adamage and wear the equipment, render proper lubrication very diill- .r cult, and requires a sacrice in vcloseness of iit u' to compensate for greater expansion of the partsI (Cl. S-161) all of which result in reduced elciency of the Dump. I If the large pumps are run at *slower than their normalspeed or if the displacement is lowered beyond a very limited amount, the capacity 6 and efficiency decreases so disproportionately that much less horespower output can be obtained fora given input by means of a larger .pump than could be obtained by a smaller pump operating at a higher speed. Obviously, in the 10 smaller pump not only are the frictional surfaces reduced but also the peripheral speed and centrifugal forces are likewise greatly reduced over those occasioned in the ylarger pumps operating'at the same angular velocity.

Another inherent disadvantage of the larger variable delivery pumps forl many applications resides in the sluggishness ofthe unit in unloading itself quickly. Assuming, for example, that a, larger'pump with necessarily less angular ve- 20 locity is used and the eccentricity set at zero or greatly reduced. necessarily a longer time is required for a complete revolution. Even assuming the pump could completely unload in one revolution therefore it is apparent that a similar higher speed pump could unload more promptly. HoweverI the eccentriclty cannot be set so promptly but must be gradually changed to" maintain a proper operating iluid pressure while unloading. Due to the much greater capacity 30 even greater delay for unloading of the pump when shifting from one setting to another is occasioned in the case of the larger pumps, even though both the larger and smaller pumps are delivering the same total iluid capacity.. As an 'example in many hydraulic press operations, a

high speed is desirablefor movingthe press into contact with the workf and thereafter a much less speed but higher pressure is required for' the forming operation. It is desirable, therefore. that 4o` a large volume of flow be provided for the idle stage of the press, followed, at the instant of engagement ofthe press with the work, with prompt unloading of the pump and setting of the pump at lesser eccentricity for building up and holding the higher pressure for the forming operation. This, of course, is important so as to obtain asmany operations of the press per minute as possible. Otherwise, the pump cannot compete with the rapid changes in speeds and pres- .50

. sures provided by mechanical gearing. A smaller pump operating at the higher angular velocities obtainable therein, 4may be unloaded and the eccentricity changed for higher pressure with no appreciable loss of time.

- hydraulic pump mechanism capable of producing,

' 'Ihe advantages of a relatively small and compact hydraulic unit of this type which can operate eiiiciently throughout an infinite variety of stages, thus providing a larger volume of ilow vat lower pressure followed almost instantaneously vantages 'above pointed'out as present in larger wide range pumps,

The present invention has as its principal objects the provision of a unit in which these disadvantages are eliminated and the provision of a pump or motor unit of this general type in which a wide range of pressures and volumes of delivery are obtainable while maintaining, at the same time, a relatively constant horsepower output and very high eiiiciency for both extremes of Y operation.

More specifically, an object is to provide a a substantially constant horespower output in the form of extremely high torque and low uid delivery and as a lower torque and higher fluid delivery, while maintaining throughout the entire range of torque and delivery combinations even to its extreme limits, the greatest eillciencies inherent in pumps and motors of this general type.

Another object is to render possible the changeovers to and fromlarge ow, low pressure cycles and the low iiowyhigh pressure cycles, quickly and efliciently.

Another object is to provide a multi-rotor pump or motor mechanism combined into a single compact unitary structure in which the pintle diameter and resultant peripheral speeds between the pintle and the rotors is kept relatively small and the centrifugal forces greatly reduced.

Another object is to provide a great range of flexibility of speeds and pressures while main-v taining a substantially constant horsepower output.

A further object is 'to provide a unitary structure including a plurality of separate pumping units cooperating with a single'pintle and connected therethrough in parallel and to a common main delivery circuit.

More specific objects reside in the provision of means for maintaining the desired synchronous relation between the cooperating rotors of the unit and a means for resisting and balancing the axial thrusts onthe rotors occasioned by the operation of the mechanism.

Another specific object is to maintain a cooperative relation between the cooperating rotors of the mechanism such that, at the higher speeds y required for high pressure, low volume delivery,

. the kinetic energy of one" of the rotors is utilized to eliminate vibration of the other and more even delivery'of iiow.

Other objects and advantages will become apparent from the following speciiication wherein reference is made to the drawings in which Fig. 1 is a horizontal sectionalview through a dual pump -or motor mechanism embodying the principles of the present invention;

Fig. 2 is a cross sectional view of the mechanism taken on -a plane indicated by the line 2--2 of Fig. 1 and also ,on a plane indicated .by the line 2'-2' of Fig. 1, -the rotor 'being slightly revolved from the position in which shown in mg. l v

Fig. 3 is a cross sectional view of the mechaprovide nism taken on a plane indicated by the line 3-3 of Fig. 1; e

Fig. 4 is a diagrammatic illustration of the flow stream of the present mechanism;

Fig. 5 is a control valve for use in connection with the mechanism; i

Fig. 6 is a diagrammatic illustration of an application of the mechanism in connection with l a hydraulic press;

Fig. 7 is a diagrammatic illustration of an application of the mechanism as a motor in circuit with a single unit conventional reversible variable delivery pump; y

Fig. 8 is a graphic comparison of the eciency of the present unit and prior structures relative to-the respective proportions of the full stroke of each; and l Fig. 9 is a reduced side elevation of a slightly modied form of the invention illustrating the utilization of diiferent size rotors in the two units forming the combination.

Referring particularly to Figs. 1 to 3 inclusive,.

the invention is illustrated in connection with a structure which may be utilized either as a pump or motor. For convenience in reference, however, the description and claims will refer to the invention as a pump, the use as a motor being readily apparent therefrom. The word pump in the claim is meant to include the structure therein recited either as a pump or motor.

vThe pump comprises a main body comprising a rigid weight supporting casing l, closed at the driving end of the pump by an end wall 2 and at the opposite end by a rigid weight supporting end wall 3. Within the casing I, and preferably integral therewith, is a partition wall or spider 4 which dividesl the casing into two sepadriven by a main drive shaft 'I from a suitable source ot power; is .mounted near Athe driving A, shaft end in a suitable set of anti-friction bearings'B. The bearings 8 are arranged on an annular axially extending hub portion 9 oi the rotor and cooperate therewith and with internal annular recesses I0 in the end cover 2 for resisting both radial thrusts and axial. thrusts tending to move the rotor toward the end cover 2. The bearings 8. are sumciently rigid to withstand ra'dial rocking of therotor.

.The rotor is provided with a set of ircumferentially spaced, radially extending, hydraulic cylinders l2 in each of which is carried a piston i4, reciprccabl radially therein. The rotor is provided with a dead end axial bore I5 which is in communication with the cylinders I2 through rotor valve ports I6 opening from the cylinders into the bore 15. IThe rotor is provided, preferably midway between its ends, with a radially extending flange I1 in which are a plurality of circumferentiallyspaced radially extending slots I8 corresponding in number .to the pistons i4, the walls oi.' which slots are parallel' to each other and to the axis of the piston with which asso- Mounted within the housing l, with its axis parallel to the axis of the lrotor 5, is a reactance housing- 2II having externalguide surfaces, cooperable with complementary guideways in the casing I, as indicated at 2i in Fig. 2, for supporting the housing 2li for movement'thereof v to different adjusted positions while maintaining the axis of the housing parallel to that of the rotor 5. vSuitable control rods 22 are secured to the housing 23 and extend to the outside of the casing through appropriate bores in the casing for shifting the housing to dispose its axis coaxial with or eccentric and parallel to the axis of the rotor 5. The rods 22, in turn, may be oper- .actance rotor 23. The reactance rotor 23 is mounted within the housing 20 preferably on anti-friction bearings 24, the races of which are spaced apart at each side of the midportion of the housing so as to accommodateitherebetween the cooperatingl head portions of the piston assemblages. 'For convenience in manufacture, assembly and service, the reactance rotor 23 preferably is formed of two axially separable annular companion members 23a and 23h, drawn by bolts 25 against the outer ends of the inner race of the bearings 24 and the ends of suitable spacers26 to form, in eiect, a unitary structure, suitable openings, as illustrated,.being provided in the flange Il to accommodate the bolts 25 and spacers 26. Fjor cooperating the pistons with the reactance rotor, each piston is provided with a crosshead 21 receivable in a corresponding one o f the radial slots I8 inthe primary rotor, which slots guide the cross-heads for radial reciprocation only and transmit thereto, along the guiding surfaces, the tangential forces resulting from operation of the mechanism. Each piston crosshead 21 is provided with a bore extending parallel to the axis of the rotor, which receives a crosspin 23the crosspin protruding beyond the crosshead at both ends. The protruding endsvv of the crosspins are received in the reactance rotor 23, anti-friction capillary needley bearings being provided between each crosspin and the walls of the bore of the piston `crosshead with which associated The rotor 6 corresponds, in form and function,

v-to the rotor and is correspondingly mounted.

A secondary rotor 3,0 and cooperating shiftable rotor housing 3|, for operating the pistons 32 o! the rotor 6, are also mounted in the casing. The remote end of the rotor 3 is carried in anti-friction bearings 33 which cooperate with an ,internal recess -in the end cover 3 for rotatably supporting the rotor 3 in a position coaxial with the rotor 5. As4 above mentioned, the rotor 5 is provided with a dead end axial bore I5, the open end of which bore is disposed toward the partition wall 4.- The rotor 6 correspondingly is provided with a dead end boreI 35 which opens toward the partition wall-4 and which is coaxial with the rotor and -with the bore l5 of the rotor 5.

For eil'ecting the proper valving relation between the .two rotors and valve' pintle means, a single stationary valve pintle 39 is provided, the pintle having a heavy shank portion 33a intermediate its ends by which it is flxedly secured in the partition wall 4. The pintle protrudes each way from the wall 4.coaxial with the bores I5 and 35, one end 39h of thepintle being received l,snugly in the bore Il'and the'other end 34e being received in the borev 35. The pintle end 39h is provided with the usual valve portion cooperable` with the corresponding portion of the wall of the bore I5 and having therein pintle ports 31 and 39 positioned to cooperate successively with the valve ports I6 of the cylinders upon rotation of the rotor 5. The end- 36e of the pintle is provided with a valve portion cooperable with the corresponding portion of the wall of the bore 35 and carrying ports 39 and 40 cooperable successively with the valve ports of the cylinders of the rotor 6. As better illustrated in `ifig. 2, the valve ports 31 and 39 of the pintle both cooperate with the same longitudinally extending ducts 4I formed in the pintle and the ports 38 and 49 communicate with the same longitudinal tion of the pump, 'may extend the full length of the pintle and be open at the free ends of the pintle so as to discharge into the dead ends of the respective bores of the rotors or, if desired, a balancing duct 44 may be provided in the pintle. The duct 44 extends entirely therethrough axially for maintaining equal hydrostatic pressures in the bores I5 and 35.

Each protruding portionof the pintle is provided both at itsshank end and free end with anti-friction capillary needle bearings cooperating with corresponding internal bearing surfaces in the rotor bore with associated for resisting hydrostatic thrusts on the pintle and maintaining it in proper coaxial and spaced relation to the walls of the bore with which it is in valving cooperation. Each protruding portion of the pintle likewise terminates in slightly spaced relation to the dead end bore Ywith which associated so that lubricant or fluid vpassing from the bore onto the valving surface pintlemay protrude thereinto as close as practicable toA the valve portion so as to insure the utmost rigidity of the pintle and provide as great strength as possible adiacent the valve surface to withstand hydrostatic thrusts, all as more fully described in my copending application, Sen-No. 5,429, filed February '7, 1935.

The secondary reactance housing for the rotor s may likewise be sinn-.ea through a medium of suitable rods 45 for varying the eccentricity of the reactance rotor 30 of the rotor 6 independently of orin predetermined xed relation to that ofthe rotor23.

The pintle shank portion 36a which is received in the'wall 4 is seal fitted thereinto and is providedwitha duct 46 with which both of the ducts 4I communicates. The partition wall 4'is drilled to provide a bore 41 directly thereinand communicating at its inner` end with the duct 43 and, at `its'outer end, with the main pressure line 43 of the mechanism. The shank 33a is also provided with a duct 49 which.communicates with the ducts 42, the partition wall being dprovided with a duct 50 which communicates at its inner end .with the duct 49 and at'its outer end with the main inlet `or feed lin of themechanism.

It is apparent that if the rotors are operated simultaneously with their secondary reactances which the pintle is disposed eccentrically in the same direction from the common rotor axis both will supply fluid under pressure to the line 4I. If, however, either the secondary reactance 2l or the reactance 30 were disposed coaxial with the rotor with which associated only one of the rotors would act as a pump` and the other ,one would be idle.

'In order to drive the rotors in the predetermined timed relationl with respect to each other so as to effect the particular result desired, the rotors are connected together by mechanical gears. Referring to Fig. 1, the rotor 5at the end adjacent the wall 4 is provided with an external helical gear 55 which preferably is positioned axially of the rotor to overlie the needle bearings adjacent the shank portion of the pintle. The rotor is correspondingly provided with a helical external gear 56 similarly arranged. Mounted within the partition` wall 4 are circumferentially spaced bushings 51 which extend parallel to the axis of the pintle. The bushings are spaced equidistant from each other and each carries longitudinally spaced sets of capillary needle bearings il through the mediumof which a driving shaft 59 is rotatably supported in each bushing. Each shaft 59 protrudes at each end beyond the wall 4 and is provided at its respective ends with helical gears 6l and 6| which cooperate respectivelywith the gears 55 and 56 of the rotors for eil'ecting the driving relation therebetween. The helical gears are so pitched that the reactance thrust on the rotors due to the driving therethrough is in a direction opposite to the thrust on the rotors due to the hydrostatic pressure Iin the respective dead end bores thereof so that the rotor bearings are relieved of as much reactance stress as possible. Thrust washers 62 are provided between each gear and the wall 4 for maintaining the gears and shafts I! and needle bearings in proper axial position. Any number of such gear connections between the rotors may be provided, two being shown herein for purposes of illustration. The sets of gearsl should be spaced circumferentially equidistant from each other,

'as statedabove, so that the driving stresses imparted by the gear teeth shall be in mechanical balance with reference to the pintle and will not tend to deflect it radially due to any mechanical unbalance. This balance can readily be effected by 'arranging the sets of gears so that for each set there is a diametrically opposite set. By helicalv gears I means generally gears whose teeth are directed other than axially, in other words, are so directed that the reactance thrust on the gears will produce an axial thrust component.

The rotors may be driven at the same speed or at different speeds depending upon the particular gear relation provided and the particular requirements of the particular job or function to be performed by 'the pump mechanism. For example to drive the rotor 6 at .a greater or less speed than the rotor 5, it is only necessary to provide a larger gear on'. one rotor and smaller gear on the corresponding end of the shaft 59. For illustrative purposes, the gears 60' and 6I and the cooperating gears 55 and 56 are shown as `cooperated for driving the rotors 5 and i at the same angular velocity.

Having in mind; that a smaller pump at high 'speed is generally more eillcient than a larger pump of the same delivery at low speed, it is obvious that with1a given power input through the Imedium of the shaft 1 and with the same high eccentricity Aoi' the secondary reactances 2l and 30, as large a volume of fluid can be delivered to the main pressure line 48 providing the pressure is not too great as with a larger pump. If merely the eccentricity of `both rotors were decreased, a higher pressure-but less volume could be obtained. If this increase were continued, the pressure could be built up but when a very low eccentricity was reached, there would be a great decrease in the emciency of the pumps. Assuming therefore, that-a large volume and low pressure were desired, both units could be set for maximum stroke and the large volume of flow at low pressure delivered. Assuming that this flow must be followed by`.a prompt increase in pressure, then the, eccentricity of the rotor 6- could be set to zero and that ofthe rotor to less eccentricity than previously operated but not so low as would be necessary were both pumps operating. s With a constant power input and idling of the rotor 6, it is apparent that the rotor 5 could bedriven at muchgreater speed and with a resonably large proportion of its maximum stroke. This would provide a much higher efliic'iency than were both the rotors driven at extremely low eccentricity. Since both pumps are small, it is apparent that they can be operated at higher angular velocity than a single larger pump of equal capacity, and the one which is idled can readily beunloaded from its oil supply much more quickly than could a larger pump. Furthermore, since the greatest eccentriclties of each of the two smaller pumps is less than would be provided in such larger pump, the time required for settingl the reactance rotors to the new positions for high pressure is' very much shorter, in fact, so short as to require no substantial delay.

Another feature that should be pointed out is that high speed and.' high pressure often create in a pump of this character a certain tendency toward vibration, due to the time elapsing between cooperation of one cylinder port and the cooperation of the next succeeding cylinder port with the same pintle port. This is due somewhat to the fact that the mass of the motor and cooperatingl parts is reduced to a minimum commensurate with the work to be done. Accordingly, much less kinetic energy is stored in the pump than would be the case were a large rotor used. Assuming the rotor I, however, is operating at high speed and the rotor E is idling, the rotor 6 provides additional mass with resultant kinetic energy for carrying the rotor past the peaks and troughs of the pressure delivery and renders the operation more uniform. When a large and small rotor are used in combination, suitable check valves may be provided in the pintle ducts to protect the larger rotor from the high pres.- sures developed by the smaller, and thus reduce the cost of the larger pump and insure full emciency of the smaller.

It isapparent that many combinations can be obtained by changing the driving gears between the rotor 5 and the rotor 6.. The range can readily be extended further by the utilization of a structure such as illustrated in Fig. 9, in which the rotors are of different sizes.

vleferring next to Figs. 4 and 5, the ilow of fluid in the unit, when operating as a pump, is illustrated diagrammatically. Assuming both rotors are driven at the same speed and are `of 7 the same' sizeand same eccentricity for each corresponding pistons again reach the ports 31 and 38. Accordingly, a fluid delivery of twice the capacity of either rotor may be obtained with the rotors operating at high speed. Assuming, however, that the rotor 6 is so set thatits eccentricity is zero it then acts as a y wheel for the rotor 5, and the only fluid delivered is delivered through the port 31.

t isl apparent that a single rotor may be run at much higher speed with moderate eccentricity to obtain an extremely high pressure instead of both rotors being run at a lower speed or at an eccentricity so low that the eiciency of both is greatly reduced'. Further, short stroke efficiency of both large and small pumps is less than full stroke eiciency. This eiect can be more readily appreciated by reference to Fig. 8. In the graph therein illustrated, the abscissa represents the proportional part of the possible stroke or eccentricity, the percentage f efficiency being represented by the ordinate. In the graphical representation the curve B represents the efiiciencycurve of `a pump or motor having a How capacity about four times that-shown by the curve A. The courve A1 is the same as A but is brought into capacity relation to curve B. Referringfto curve B, it is apparent that when the eccentricity if 11g of the total, the eiiiciency is only 30% as indicated by the point e; for eccentricity 1A; the efliciency is about 48% as indicated by the point f; for eccentricity the efviiciency is about 61% indicated by the point 'g and for 1A eccentricity the eiilciency is about 68%. Not until the eccentricity is about half the total does the eihciency reach 80%. While delivering the same capacity of ow, at these lower limits, a smaller pump, indicated by the curve A1, will reach about 63% eiiiciency for a capacity at which the larger pump Awould be operating at about 30%. It is obvious to reference to the points a', b', c' and d' that the efiiciency of the smaller pump increases far more rapidly for capacities equalto those delivered by the larger pump when the latter is operating at less than 50% eccentricity. Therefore two smaller pumps operating at be much more efficient than a large pump of capacity equal'to the two and operating at 1/4 or less eccentricity. Furthermore, by idling one Dump. plied to the other and operate it at an eccentricity commensurate with high efciency while maintaining a low ilow, high pressure delivery.

As one exemplary use of the invention, it is diagrammatically illustrated in Fig. 6 for use in connection with a hydraulic press in which a large ow and corresponding movement of the press is required preparatory to engagement with the work and a much higher pressure but less flow is required for the forming operation.' It

parent that with this structure both therotors 5 and 6 can be operated concurrently to provide for the initial movement of the press until thepress has engaged the work. rIjhereafter the rotor 6 can be set at zero eccentricity and the high pressure for the forming operationperformed by the rotor 5. In this operation the iiow from the unit passes along the main line 4 8 into a control valve 10 from which it passes into the feed line 1I for supplying pressure 'I2 of the press. Fluidin front of the piston concurrently discharges throught the line 13 and through` the valve 18 and line 14 to a feed sump 15 higher eccentricity would the total inputof horsepower can be apis apto the piston from which it is drawn through the line 5l into the unit. The control valve 10 is better illustrated in Fig. 5. The valve 10 comprises a body having a main inlet 16 connected to the main feed line 48 of the mechanism for supplying iiuid under pressure thereto. Within the body is a main bore 11 with which the passage 16 communicates. Likewise communicating with the bore 11 are passages 18 and 80, these passages opening into the bore 11 at opposite sides of the opening of the passage 16 thereinto. The passage 19 communicates with the line 1I leading to the working side of the piston 12 and the passage 80 communicates with the line 13. At the ends of the bore 11 are ducts 8| and' 82 which communicate with a main trunk line 83 which, in turn, communicates with the line 14. Mounted in the 18 is a valve rod 84 onwhich are carried sleeve valves 85 and 86 snugly received with a hydraulic t in the bore 11 and spaced apart from each other longitudinally thereof. The sleeve valves 85 and 86 are of sufficient diameter to close that portion of the bore 11 in which received. The passages 7S, .18 and 80 are spaced apart equal distances, such distance being slightly greater than the lengths of the sleeve valves 85 and 86. Qbviously, when the valve is set in the position illustrated in Fig. 5, fluid delivered from the feed line 48 can flow only to the line 1| leading to the pressure side of the piston. The iluid at the opposite side of the piston discharging through the line 13 enters the valvey through the passage 88 and can pass through the ducts 82 and 83 to the discharge line '14, the .valves 85 and 88 preventing passage of fluid from either passage 16 or 18 into the duct 83. To reverse the piston-- 12 the valve stem is pulled to the right, this operation communicating the line 13 with the line 48 thus forcing the iluid to the lead side of the piston. Concurrently line 13 is prevented from communication with the duct 83 and the passage 16 is Aprevented from communication with the passage 19. The uid on the force side of the piston 12 therefore is discharged through the line 1| and through the duct 8| into the main' trunk 83 from which it passes into the line 14. It is apparent that by using a Servo-motor, it is a simple matter to control the eccentricities of the two pump units herein shown in response to actions of the press, a simple lever connection between the press and Servo-motor being provided to idle the rotorV 6 when the press engages the work for the forming operation.

Referring next to Fig. 7, the operation of the unit as a motor is illustrated, uid under pressure being supplied from a suitable sump S to a reversible variable delivery pump P, 'the pressure line of which is designated 86, .the suction side beingrl designated 81. Fluid, under pressure therefore is forced from the pump into the passage 48 of the unit and thereby drives the rotors 5 Iandl 6 concurrently and is discharged therefrom through the pasage 5I which, when the unit was operating as a pump, was the suction passage. From the passage 5I, in turn, the uid will' be conducted to the suction 81 line of the pump. A check valve V is provided in the line 81 between the sump and junctureJ with the line 5l tol assure anadequate-supply of iiuid and thus replace any lost by slippage through the device. Instead of the pump P, a multi-stage reversible variable delivery pump, the same as' the motor of Fig. 7, may be employed, in which combination the eigective range and possible variations are innitely increased.

It is apparent therefore that with the u nit described andthe variations set forth, an extremely wide range of flow and pressure and a wide range of combinations can be' provided froma substantially constant horsepower input and that the total horsepower input can be translated either intovlarge volume of flow or high pressure at a substantially constant horsepower output and high emciency throughout, the only llosses occurring being those inherent in hydraulic pumps and motors even when operating at their highest eiiiciency. While I have described, for purposes of illustration, the use of the present inventionv in connection with a reciprocatory press operated at various stages, it is readily apparent that great advantages can be obtained with the present pump or motor as a constant horsepower transmission device in numerous kinds of machinery, such as automobile transmissions, machine tools, excavators, cranes and in such apparatus as utilizes Diesel power engines as prime movers. The advantages reside largely in the fact that in these various types of apparatus the eiiciency of Y the prime mover itself is developed to the highest ii' it can be operated at its rated speed constantly.

I claim:

A multi-stage hydraulic pump t motor comprising a pair of coaxial rotary radial piston stage units, each unit including a. rotor having a closed end valve bore, piston and cylinder assemblies for each rotor, reactance means for the asemblies respectively for actuating the same, means rotatably mounting said rotors in spaced relation axially from each other and with the valve bores coaxial and opening toward each other, a rigid support between the rotors. a valve pintle xedly secured in said support and extending in opposite directions therefrom into the respective bores of the rotors and being in valving relation with the respective asemblies, whereby hydrostatic reactance thrusts result in said bores urging said rotors axially apart, a rotatable shaft mounted in said support, helical gears respective to the ends oi' said shaft and'iixedly secured thereon, cooperating gears on the rotors respectively for drivingly connecting the rotors together mechanically, and said gears being helically pitched to cause reactionary thrusts urging the rotors axially toward each other, and impeller means forl one of said rotors and coaxial therewith.

ELEK K. BENEDEK. 

